The present invention relates to multiple sprocket assemblies for bicycles, and more particularly, to a multiple sprocket assembly including a smaller sprocket and a larger sprocket connected by pins.
A multiple sprocket assembly mounted to a rear wheel is one of the main components of a drive train for mountain and racing bikes. Multiple sprocket assemblies may include as many as eleven sprockets. The sprockets are highly loaded components and thus are subject to wear. Conventional sprockets have an inner contour with a torque-transmitting profile that is mountable to a driver of a cassette hub or to an outer ring of a freewheel hub. The spacing between adjacent sprockets is critical for shifting the bicycle chain from one sprocket to the adjacent sprocket and is determined by how the torque-transmitting profile on the sprockets engage the driver or the outer ring of the freewheel hub. The sprockets are also subject to an undesirable bending load as a result of oblique chain tensile forces.
One development trend in multiple sprocket assemblies is weight reduction. This objective may be achieved, while still satisfying the mentioned basic requirements, by support elements such as spiders disposed between the sprockets and the driver. However, the achieved weight reduction is then limited.
To reduce lateral bending of individual sprockets, pins may be used to support the sprockets relative to each other. For example, the document JP 59-165293 discloses the use of such pins on a freewheel hub and documents, DE 10 2007 010 456 and DE 10 2007 006 852 disclose use of such pins on a cassette hub. Further, document DE 102 60 565 discloses a multiple sprocket assembly having a spider with a third sprocket riveted to the largest sprocket, in addition to the two sprockets.
The document EP 2 045 181 discloses a multiple sprocket assembly including individual sprockets radially supported on a driver and connected to each other by a spacer element. The individual sprockets are fastened to the spacer element. The connecting holes on the individual sprockets are determined by connecting holes on the spacer element.
Another approach to minimize weight is disclosed in document DE 10 2008 010 904. The individual sprockets are formed as one piece from a single blank by turning and milling operations. This involves a gradation of number of teeth with larger differences in the number of teeth, as it given priority during use for a mountain bike. The support structure of the sprocket assembly forms a hollow element in the shape of a cone. The sprockets are not supported on a “spider” adapter relative to a driver on the rear wheel hub. Instead, the hollow cone element contacts and is supported driver at two positions axially spaced from each. The hollow cone element includes annular support elements having an annular cylinder and an annular disc. Openings between the annular support elements permit passage of dirt and sludge. Dirt accumulation beneath the chain engaging on the sprocket can be avoided by these openings. Otherwise the chain would force dirt patches on the sprocket inward and compress and consolidate them there. The consolidated dirt accumulations can increasingly grow in the radial direction and increasingly force the chain outward until the chain no longer properly engages on the sprocket teeth and finally jumps off. Despite its very low weight, the support structure is sufficiently rigid and solid so that interfering larger deformations and breaks as a result of the drive force of the chain may be avoided.
One disadvantage of the above sprocket assembly is the high cost of manufacture by machining methods of turning and milling. Accordingly there is a need for a multiple sprocket assembly having both reduced weight, satisfies the strength and rigidity requirements and is simple and cost-effective to manufacture.